Reset object origin without moving object
Here's one way which assumes your object is centered over 0,0,0:


Snap the 3D cursor to the object's origin (&#8679; ShiftS)
Depending on the orientation of your object, set the 3D cursor's location to 0 along one axis (based on your screenshot you'll want to set it to 0 on the Y axis)
Snap the origin to the cursor (&#9096; Ctrl&#8679; Shift&#9095; AltC)





Apply rotation (&#9096; CtrlA) to vertices (this will reset object rotation).